The present invention relates to a device for the angular setting of a scale mounted on a head of a universal parallel ruler.
In the universal parallel ruler of prior art, a square comprising a horizontal scale and a vertical scale is rotatably supported in a stationary support on a ruler head so that said square may be set to a position deviating by a desired angular distance from a basic line position at which the horizontal scale is horizontally located and the vertical scale is vertically located on the drawing board. The amount of such angular deviation or rotation of the square is usually read from a protractor mounted on said stationary and a vernier mounted on the square. Recently it has been proposed to read this amount from an electric digital display means comprising an encoder interposed between the stationary support and a rotatable portion on the side of said square. However, with the conventional methods and means as mentioned above, the operator must rotate the square or scale to a desired angular position to effect a desired angular setting of the scale, following the protractor's graduations or the digital value, both of which continuously vary as the scale is rotated thereby requiring the user's concentrated attention.
In accordance with the present invention, these disadvantages associated with the conventional device are eliminated. The present invention comprises a universal parallel ruler including a device for angular setting the scale, in which, when a desired angle of rotation is applied by the operator into an input station, this angle is digitally displayed on a display station and simultaneously this input signal is supplied to a comparator to which is also supplied an output signal from a detector adapted to detect an actual angular position of the scale, said comparator providing, when the scale has been correctly set to the desired angular position, a coincidence signal in accordance with which a display lamp or the like of a display station is lit so that the operator may set the scale to the desired angular position simply by observing this display.
In addition, the present invention also includes a device for angular setting the scale, in which, when a desired angle of rotation is supplied by the operator to an input station, this angle is digitally displayed on a display station and simultaneously this input signal is supplied to a comparator to which is also supplied an output signal from a detector which is adapted to detect an actual angular position of the scale. When the scale has been correctly set the desired angular position, the comparator provides a coincidence signal which in turn activates a braking means such that the operator may set the scale to the desired angular position simply by rotating the scale.
Accordingly, a principal object of the present invention is to overcome the drawbacks of the prior art device by providing a device for angular setting the scale of a parallel ruler such that, when a desired angle of rotation is given to the device as an input signal, this angle is digitally displayed by a display means and the angular setting of the scale is immediately completed.
An additional object of the present invention is to provide a device for angular setting the scale utilizing various means for automatically preventing the scale from being rotated once the scale has achieved its desired position and means for freely establishing a position to which the scale has been rotated by a given angle as a basic line position of the scale, means to prevent the scale from being further rotated beyond a limit position even when a scale setting beyond this limit is intended, means enabling a scale setting with addition or subtraction of a desired angle to or from a given angle of previous rotation, and means for provisionally setting a position corresponding to rotation of the scale by a given angle.
Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter; it should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modification within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.